[jbosscache-dev] Re: Cache Loaders and Non-String Fqns - Was: 2.0.0.BETA2

[Brian Stansberry]

Manik Surtani wrote:
> 
> On 15 Mar 2007, at 18:24, Brian Stansberry wrote:
> 
>> Manik Surtani wrote:
>>> I think we're going to need to support non-String Fqns.  We're not 
>>> going away from that anytime soon.  :S
>>
>> Good.  I'm not positive, but I think the only place non-String Fqns 
>> are irreparably broken is with a preload call to a cache loader.
> 
> Well, any config file element that uses Fqns.  Eviction policies, for 
> example.  But that's a limitation on the config file, nothing else.
> 

We should think about improving handling this for configurations built 
by a DI framework.

>> With other cache loader calls, the real fqn is available as a call 
>> parameter, so the string-based representation used for the persistent 
>> store doesn't have to leave the cache loader.
> 
> Yeah, that can be worked around.  What do you reckon the best approach 
> for "encoding" Fqns are, for CLs that only use Strings?
> 
> For each Fqn element, "Type:" + element.getClass() + ":value:" + 
> element.toString() ?

Not sure why what we do now isn't sufficient (confession - haven't 
really looked).

> 
> Could barf with user objects that don't override toString() and you have 
> object hash codes...
>

Yeah, if element.toString() doesn't provide a stable, unique id for 
element, then element's type is not appropriate for use in an Fqn with a 
cache loader.

This is a bit complex, but can be summarized in a prominent doc page 
(and javadoc) on Fqn:

1) If cache is LOCAL with no cache loader, any Object will do.
2) If cache is replicated with no cache loader, any Serializable will do.
3) If a cache loader is used, for each type 'element' in the Fqn 
element.toString() must provide a stable, unique id for element. Default 
Object.toString() is no good; most (if not all) java.lang.Number classes 
are fine. A toString() impl that lists the class and the field 
name-value pairs for all the fields that go into an equals() evaluation 
is good.
4) If a cache loader is used and you want to use preload, the type must 
be String.

> CC'ing dev list, BTW.
> 
> -- 
> Manik Surtani
> 
> Lead, JBoss Cache
> JBoss, a division of Red Hat
> 
> Email: manik at jboss.org
> Telephone: +44 7786 702 706
> MSN: manik at surtani.org
> Yahoo/AIM/Skype: maniksurtani
> 
> 


-- 
Brian Stansberry
Lead, AS Clustering
JBoss, a division of Red Hat
brian.stansberry at redhat.com